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Agency of Agriculture’s State Veterinarians Urge Horse Owners to Vaccinate for Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV)

Spring is around the corner, and with its arrival comes the need for horse-owning Vermonters to ensure that their companions are protected from diseases transmitted by mosquitos, such as Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV).

EEE is a mosquito-borne, viral infection that can cause severe neurologic disease in horses, with mortality rates approaching 100. Although horses are the animals most susceptible to EEE, the virus can cause disease in other mammals such as llamas and alpacas and in emus. In all animals, the onset of clinical signs is generally three to ten days after a bite by an infected mosquito. Mammals infected with EEE most commonly exhibit neurologic signs including ataxia or incoordination, inability to stand, limb weakness or paralysis, seizures and death, while infected emus often develop hemorrhagic diarrhea. WNV infection can cause similar signs in horses, although those signs are often less severe, and the mortality rate that results from WNV infection is generally lower than that associated with EEE infection. Mammals infected with EEE and WNV are dead-end hosts, meaning that they generally are unable to transmit the diseases to other animals or to people. Vermont cases of EEE and WNV are required to be reported to the Office of the State Veterinarian.

“This is the time of the year when horse owners should be consulting with their veterinarians to ensure that their horses are appropriately vaccinated for EEE and WNV”, says Dr. Kristin Haas, Vermont State Veterinarian. “A horse’s susceptibility to EEE and WNV infection is not linked to travel to shows, fairs or other commingling events,” she adds. “We know that both viruses are present in Vermont, so even horses that spend the majority of their time on isolated properties are susceptible and should be vaccinated.”

Although vaccination is the most effective tool for preventing EEE in horses, owners may also protect their horses from infection by using an acceptable insect repellent seasonally and mechanical barriers such as fly sheets and face nets. Changing out water troughs regularly and removing other items that hold water will help to reduce mosquito breeding areas.

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About the Vermont Agency of Agriculture, Food, and Markets: VAAFM facilitates, supports and encourages the growth and viability of agriculture in Vermont while protecting the working landscape, human health, animal health, plant health, consumers and the environment.